mem-cache: Remove a std::move clang says is unnecessary.

It also says it prevents an optimization.

Change-Id: I9c21dc1a0c53cf70cefd1400564de07d1e845a75
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23124
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/cache/compressors/cpack.cc

@@ -63,7 +63,7 @@ CPack::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
     decomp_lat = Cycles(blkSize/8);
 
     // Return compressed line
-    return std::move(comp_data);
+    return comp_data;
 }
 
 CPack*